1. Field of the Invention
The present invention relates to a mobile communication system, a mobile communication method, and a mobile communication terminal. More specifically, the present invention relates to a technique to monitor neighboring cells of a cell in which a mobile communication terminal (that is, a mobile station) is located.
2. Description of the Related Art
In a mobile communication system applying the Wideband Code Division Multiple Access (W-CDMA) technology, a mobile station always monitors reception levels of a currently located cell and neighboring cells thereof so as to execute handover and cell reselection. However, when the mobile station always monitors the neighboring cells, operation rate of the mobile station becomes higher and power consumption thereof increases. Accordingly, there is proposed a mobile communication system which does not monitor signals of neighboring cells when a reception signal level of a signal received from a base station of the cell in which the mobile station is currently located is sufficiently large. This system is described in 3GPP TS25.304 v5.3.0 (2003-06) pages 18-24 and in 3GPP TS 25.301 v5.5.0 (2003-06) pages 408-412, for example. However, when the mobile station moves at high speed, speed of a decline of the reception signal level is greater than an operation cycle for monitoring the neighboring cells. Cell reselection of the mobile station is delayed as a result. When the cell reselection is delayed, the mobile station cannot send and receive a call.